OVERVIEW OF DIGITAL IMAGING AND RADIATION PROTECTION ISSUES

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OVERVIEW OF DIGITAL IMAGING AND RADIATION
PROTECTION ISSUES

• Robert M. Gagne
• MICAB/DECS/OST
• rmg_at_cdrh.fda.gov

From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
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What is the purpose of this presentation?

• Here are a couple reasons
• interest in digital imaging!
• some concerns related to radiation safety and
  effectiveness
• potential for exposure increase (and/or
  reduction??)
• Forces a re-visit of some actions in the far
  radiological health past
• imaging system inefficiency
• Review of options (regulatory or otherwise) for
  dealing with actual and/or perceived concerns

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What kind of equipment?

• Digital radiography (DR)
• not digital fluoroscopy using CCD cameras
• not film digitizers
• Three different types of DR systems
• flat panel imaging arrays
• computed radiography systems
• CCD based - optically coupled systems

What are the concerns?

• No equivalence to "speed" or self limitation as
  in screen/film systems
• Inefficient" systems possible?

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Flat Panel Imaging Arrays(indirect conversion)
From Medical Imaging, 2000
Image Formation
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
5
Flat Panel Imaging Arrays(direct conversion)
From Medical Imaging, 2000
Image Formation
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
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Flat Panel Imaging Arrays
Number of Pixel Elements (3000 x 2500)
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
Pixel Element Size ( 0.14 mm x 0.14 mm )
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
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Computed Radiography
Image Formation
From Handbook of Medical Imaging, Volume I.,
Chapter 5, M. Yaffee, eds, SPIE Press 2000
Pixel Elements ( 0.2 mm x 0.2 mm )
Pixel Elements (2160 x 1800)
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CCD based - lens coupled DR system
From P. Sund et al, Proc. SPIE 3977 437 2000
CCD based - fiber optic coupled DR system
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
Pixel Elements (3000 x 2500)
Pixel Element ( 0.14 mm x 0.14 mm )
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What are radiation protection and safety issues?

• Unique characteristics of screen/film imaging
  systems
• self limitation of patient exposure
• concept of "speed" defined and understood
• New considerations for digital radiography
• no self limitation as in screen/film systems
• no consensus on speed
• "inefficient" systems possible?

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Film/Screen Self Limitation

• Imaging task with large dynamic range
• Be careful not to under or over expose film
• Self limitation of patient exposure

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Film/Screen Speed
Difference in speed of about 2

• Film/screen speed
• speed 100/E where E is exposure in mR to
  produce an optical density of 1.0
• position on exposure axis dependent on speed
• higher speed number translates to lower patient
  exposure

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DR Speed

• DR operating point
• equivalence to film/screen speed set at
  installation?
• no self limitation except at extreme ends of
  the gray-scale transfer curve
• patient exposure increase / decrease /
  equivalence compared to film/screen?

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Imaging System Inefficiency

• Chest radiography - screening program (60s-70s)
  for cardiopulmonary disease
• need for rapid, economical imaging system
• Photofluorographic (PFG) imaging system
• mobile vans

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Public Health Concerns

• Low detection rate for tuberculosis, heart
  disease, and other respiratory diseases
• High patient radiation exposure vs conventional
  screen/film radiography
• BRH develops standard technique for estimating
  patient exposure

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Digital Radiography (CCD based - lens coupled)

• Careful system design to overcome inefficiencies

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Level of Public Health Concern
From Medical Imaging, 2000

• Installation base is small (even smaller for CCD
  based - lens coupled systems)
• computed radiography not included
• Basic questions Is there evidence of higher
  patient radiation exposure with these imaging
  systems screen/film radiography?

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Options

• Tracking exposure levels
• NEXT 2001 chest radiography
• diagnostic reference levels (ICRP, AAPM, many
  others)
• practical tools for managing radiation dose
  levels to patients
• Quality assurance programs
• Performance evaluation of Computed radiography
  system, Med. Phys. 28(3), March 2001
• Diagnostic x-ray Performance Standard
• performance requirements on levels of imaging
  performance such as detective quantum efficiency
  (DQE)
• dose display at operators console

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Dose Display

• Previous slide describes several viable options
• TEPRSSC radiation standards and safety
  committee
• Diagnostic x-ray Performance Standard
• dose display at operators console for all
  radiographic equipment
• Practical considerations yet to be explored or
  evaluated
• cost
• effectiveness
• alternatives?
• dose descriptor and definition?
• tie to diagnostic reference levels
• effective resource allocation

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Summary

• Different types of DR
• flat panel imaging arrays
• computed radiography systems
• CCD based - optically coupled systems
• Radiation safety and effectiveness issues
• no equivalence to "speed" as in screen/film
  systems
• "inefficient" systems
• present revisits the past
• potential for exposure reduction and/or
  increase??
• Options for dealing with perceived and/or actual
  concerns
• one suggested regulatory approach